What Wizard69 says is correct. In planning for construction or mounting a JIb crane be it a freestanding or mounted to an existing structure the forces acting on the type of mounting increase exponentially with each foot out from the center of the pivot
here is a link to a 3 ton free standing crane I built many years ago to meet the MIL spec requirements everything associated with the crane itself excepting for the actual hoist was required to be tested to a load of double the rated capacity take special note of the excavation for the base mount
3 ton free standing jib crane